What problem does this calculator solve?
Savers and business owners want to understand how interest, time, and regular deposits can affect a balance. Our calculator shows the result of a stated scenario rather than forecasting returns.
Contribution timing and rate conventions affect a savings model differently. This calculator exposes its monthly-equivalent rate and separates contributed money from modeled interest.
Six practical questions, answered clearly
Find the calculation behind your question. These answers explain how to use the inputs and results when making a decision.
How can compound interest change my starting balance?
Interest already credited earns interest in later periods. At a positive rate, that reinvestment can make growth accelerate over time.
What could monthly deposits add up to over ten years?
The calculator combines starting capital, monthly contributions, the term, and the assumed rate. It shows the modeled ending balance separately from the amount contributed.
How does simple interest differ from compound interest?
Simple interest applies only to the original principal. Compound interest also applies to previously credited interest.
What happens if I use a higher interest rate?
With other assumptions unchanged, a higher positive rate produces a higher modeled ending balance. It does not make that rate achievable or guaranteed.
How much of my ending balance comes from deposits?
The calculator displays total contributed capital separately from the modeled interest result.
Why does the investment term matter for compounding?
A longer term gives interest that has already accumulated more periods in which to earn further interest. Outcomes still depend on the assumed rate and costs excluded from the model.
Worked example
Without contributions, €1,000 at an effective 5% annual rate becomes €1,102.50 after two years. At 0%, €1,000 initially plus €100 monthly totals €2,200 after one year.
Formula and calculation method
Calculate using your own assumptions
Enter values in a single currency. Results update as you change inputs. Save up to three scenarios for this session. Copy and CSV export include the assumptions and explanations used.
Practical use cases
- Separate contributed savings from modeled interest.
- Compare beginning- and end-of-month deposits.
- Convert a nominal rate to an effective annual rate.
Assumptions and limitations
Monthly-equivalent model, not day-accurate bank-account accounting. Constant rate; excludes taxes, fees, and inflation. One to sixty whole years. Negative rates down to −99% can be modeled. No guaranteed return.
Further official information
FAQ: Using the tool, capabilities, and calculation limits
Is this compound interest calculator free?
Yes. It works without registration.
Can I include regular monthly deposits?
Yes. Monthly contributions can be included at the beginning or end of the month.
Does the calculation include taxes and inflation?
The standard calculation shows nominal monetary values before taxes and inflation. These monetary values are distinct from the choice between a nominal and an effective interest rate. Any additional assumptions would need to be stated explicitly.
Are the calculated returns guaranteed?
No. They follow an assumed interest rate and are a mathematical scenario.
Can I see the balance for each year?
Yes. The calculator provides an annual table and a CSV export.
How does a balance develop with monthly deposits?
The model applies a constant equivalent monthly rate and places each deposit at the chosen beginning or end of the month. The annual table separates contributions from interest.
How do nominal and effective rates differ?
A nominal annual rate requires a compounding frequency. The effective annual rate includes that compounding. An entered effective rate does not receive another compounding adjustment.
Why does a beginning-of-month deposit change the result?
It participates in that month’s modeled growth. End-of-month contributions arrive after interest is applied. Negative rates can reverse the benefit.
How are monthly deposits modeled with annual compounding?
An equivalent monthly rate is derived from the annual rate. This provides a consistent convention between posting dates; a bank may calculate deposit timing and interest days differently.
Is the ending balance a promised investment return?
No. It follows constant assumptions. Markets, fees, taxes, inflation, and account terms can materially change actual outcomes.
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Request a free, nonbinding consultation →Calculation model V1.1 · Formulas maintained with the tool · editorial update: November 9, 2026.